A steel can, tin can, tin (especially in British English, Australian English, Canadian English and South African English), or can is a container made of thin metal, for distribution or storage of goods. Some cans are opened by removing the top panel with a can opener or other tool; others have covers removable by hand without a tool. Cans can store a broad variety of contents: food, beverages, oil, chemicals, etc. In a broad sense, any metal container is sometimes called a "tin can", even if it is made of, for example, aluminium.

Steel cans were traditionally made of tinplate; the tin coating stopped the contents from rusting the steel. Tinned steel is still used, especially for fruit juices and pale canned fruit. Modern cans are often made from steel lined with transparent films made from assorted plastics, instead of tin. Early cans were often soldered with high-lead solders, which could and did cause lead poisoning.

Cans are highly recyclable and around 65% of steel cans are recycled.

History

The Dutch are noted as the first to tin food, their Navy being reported as carrying cleaned and brine cooked salmon, in tin plated, iron boxes, as early as 1772.

French inventor Nicholas Appert experimented with food preservation in glass containers, in the early 1800s. Frenchman Philippe de Girard, had British merchant Peter Durand obtain an English patent for the process in 1810. Durand did not pursue food canning, but, in 1812, sold his patent to two Englishmen, Bryan Donkin and John Hall, who refined the process and product, and set up the world's first commercial canning factory on Southwark Park Road, London. By 1813 they were producing their first tin canned goods for the Royal Navy. By 1820, tin canisters or cans were being used for gunpowder, seeds, and turpentine.

Early tin cans were sealed by soldering with a tin–lead alloy, which could lead to lead poisoning. Automated soldering machines started to arrive in the 1870s and steel started to displace iron as a material for the cans at the very end of the 19th century. Locking side seam was invented by Max Ams in 1888, giving the rise to a "sanitary can" design, where the solder was found only on the outside of the can and never touched the food. The modern three-piece design dates back to 1904 (Sanitary Can Company of New York).

In 1901 in the United States, the American Can Company was founded, at the time producing 90% of the tin cans in the United States.American Can Company: Revolution in Containers , Excerpts of William C. Stolk; Address of The Newcomen Society of North America, April 21, 1960 – Printed July 1960, from oilcans.net, retrieved 16 July 2010 It bought out the Sanitary Can Company of New York in 1908, and the three-piece design displaced all other cans by the early 1920s. The can saw very little change since then, although better technology brought 20% reduction in the use of steel, and 50% - in the use of tin (the modern cans are 99.5% steel).

Canned food in tin cans was already quite popular in various countries when technological advancements in the 1920s lowered the cost of the cans even further. In 1935, the first beer in metal cans was sold; it was an instant sales success. The production of these three-piece cans by the American Can Company stopped for World War II due to lack of material, after the war the first Cone top. The use of aluminum started in 1958 with Primo beer.

About 600 different types of cans were used in the early 21st century, with the most popular being the three-piece design with side seam and two double-seamed ends, followed by the two-piece construction with sides and bottom drawn as one piece.

Description Most cans are right circular cylinders with identical and parallel round tops and bottoms with vertical sides. However, in cans for small volumes or particularly-shaped contents, the top and bottom may be rounded-corner rectangles or ovals. Other contents may suit a can that is somewhat conical in shape.

Fabrication of most cans results in at least one rim—a narrow ring slightly larger than the outside diameter of the rest of the can. The flat surfaces of rimmed cans are recessed from the edge of any rim (toward the middle of the can) by about the width of the rim; the inside diameter of a rim, adjacent to this recessed surface, is slightly smaller than the inside diameter of the rest of the can.

Three-piece can construction results in top and bottom rims. In two-piece construction, one piece is a flat top and the other a deep-drawn cup-shaped piece that combines the (at least roughly) cylindrical wall and the round base. Transition between wall and base is usually gradual. Such cans have a single rim at the top. Some cans have a separate cover that slides onto the top or is hinged.

Two piece steel cans can be made by "drawing" to form the bottom and sides and adding an "end" at the top: these do not have side seams. Cans can be fabricated with separate slip-on, or friction fit covers and with covers attached by hinges. Various easy opening methods are available.Soroka (2002) Fundamentals of Packaging Technology, Institute of Packaging Professionals

In the mid-20th century, a few milk products were packaged in nearly rimless cans, reflecting different construction; in this case, one flat surface had a hole (for filling the nearly complete can) that was sealed after filling with a quickly solidifying drop of molten solder. Concern arose that the milk contained unsafe levels of lead leached from this solder plug.

Advantages of steel cans A number of factors make steel cans useful containers for beverages. Steel cans are stronger than cartons or plastic, and less fragile than glass, protecting the product in transit and preventing leakage or spillage, while also reducing the need for secondary packaging.

Steel and aluminium packaging offer complete protection against light, water and air, and metal cans without resealable closures are among the most tamper-evident of all packaging materials. Food and drink packed in steel cans has equivalent vitamin content to freshly prepared, without needing preserving agents. Steel cans also extend the product's shelf-life, allowing longer sell-by and use-by dates and reducing waste.

As an ambient packaging medium, steel cans do not require cooling in the supply chain, simplifying logistics and storage, and saving energy and cost. At the same time, steel's relatively high thermal conductivity means canned drinks chill much more rapidly and easily than those in glass or plastic bottles.

Materials and health issues

Tin No cans currently in wide use are composed primarily or wholly of tin. Until the second half of the 20th century, almost all cans were made of tinplate steel. The steel was cheap and structurally strong, but prone to rust; the tin coating prevented the wet food from corroding the steel. Corrosion-resistant coatings on almost all steel food cans are now made from plastic, not tin. Some manufacturers use Vitreous enamel, instead.

Dissolution of tin into the food Tin is corrosion resistant, but acidic food like fruits and vegetables can corrode the tin layer. Nausea, vomiting, and diarrhea have been reported after ingesting canned food containing 200 mg/kg of tin. A 2002 study showed that 99.5% of 1,200 tested cans contained below the UK regulatory limit of 200 mg/kg of tin – an improvement over most previous studies, which was largely attributed to the increased use of fully lacquered cans for acidic foods. They concluded that the results do not raise any long term food safety concerns for consumers. The two non-compliant products were voluntarily recalled.

Evidence of tin impurities can sometimes be indicated by discolored food (pears, for example), but lack of color change does not guarantee that a food is not tainted with tin.

Lead Lead is harmful to health in any quantity. Infants and children are more severely affected, as lead harms brain development.

In November 1991, US can manufacturers voluntarily eliminated lead seams in food cans. Imported food cans continued to include lead soldered seams.

In 1995, the US FDA issued a rule prohibiting lead soldered food cans, including both domestic and imported food cans.

Plastic linings Many metal food cans are lined with plastic, to prevent the food from corroding the can.Update on can lining changes Industry explainer These linings can leach contaminants into the canned food. Some of these contaminants are substances with known health harms, though whether they are ingested in canned food in levels sufficient to cause harms is not known.UK Food Standards Agency is unsure of harms to humans. Review finding canned food consumption is a predictor of urine BPA. Market survey of the materials in can linings, including BPA-free substitutes. Review discussing migration of contaminants in canned food from can materials Update on can lining changes Washington State, in the US, looking at improving the safety of can linings., and specifically

Among other substances, the plastic linings in food cans often contain bisphenol A (BPA).https://www.fr.de/verbraucher/konserven-bisphenol-richtwerte-eu-lebensmittel-stiftung-warentest-bpa-belastung-93035126.htmlhttps://www.br.de/nachrichten/wissen/warentester-51-von-58-konserven-mit-bisphenol-a-belastet,UAxijMYhttps://www.mz.de/leben/gesundheit/gesundheitsgefahr-viele-konservendosen-geben-bisphenol-a-ab-3832189https://www.bund.net/themen/chemie/hormonelle-schadstoffe/bisphenol-a/lebensmittelkonserven/ Pregnant women who eat more canned food have higher levels of BPA in their urine.

Other constituents in can linings, including newer BPA-free can linings, have also been identified as having known health harms.Market survey of the materials in can linings, including BPA-free substitutes. Review discussing migration of contaminants in canned food from can materials Update on can lining changes Industry explainer an industry-run market survey showing only some cans imported to the US now contain BPA, as of 2020. Washington State, in the US, looking at improving the safety of can linings., and specifically

Bisphenol-A

Bisphenol-A (BPA) is a controversial chemical compound present in commercially available tin can plastic linings and transferred to canned food. The inside of the can is coated with an epoxy coating, in an attempt to prevent food or beverage from coming into contact with the metal. The longer food is in a can, and the warmer and more acidic it is, the more BPA leaches into it. In September 2010, Canada became the first country to declare BPA a toxic substance. In the European Union and Canada, BPA use is banned in baby bottles. The FDA does not regulate BPA (see BPA controversy#Public health regulatory history in the United States). Several companies, like Campbell's Soup, announced plans to eliminate BPA from the linings of their cans, but have not said which chemical they plan to replace it with. (See BPA controversy#Chemical manufacturers reactions to bans.)

Canada In 2016, BPA was common in food can linings in Canada. , Health Canada's Food Directorate concluded that "the current dietary exposure to BPA through food packaging uses is not expected to pose a health risk to the general population, including newborns and infants". They also stated that, as some animal studies had shown effects from low levels of BPA, they were seeking to make BPA levels in food packaged for infants and newborns (especially formula). They also cited a WHO review.

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